GNS3 is a visual design tool and front-end to access emulated routers.
It can export graphical network maps (with a reasonable set of icons for
simple diagram-creations needs), control Dynamips and QEMU instances
(including adding and removing connections between nodes) and more.

Control over QEMU nodes is particularly nice; by default GNS3 uses
a "base" disk image, allowing simple and disk-efficient creation of
large networks based on a common operating system.
